“OK, I’m an explorer. I enjoy doing research!” — Richard Feynman, one of the most influential scientists of the 20th century, had a legendary curiosity. His unconventional and enthralling physics lectures established his fame among students and seekers all over the world before he was awarded the Nobel Prize in 1965. However, his excessive zest for life made him an American cultural icon; here was a mind of remarkable intelligence devoted to the idea that the excitement of discovery was rivaled only by the joy of sharing it with others. We are able to glimpse this side of Feynman like never before in this career-spanning collection of letters, many of which are published here for the first time. Perfectly Reasonable Deviations from the Beaten Track spans a dizzying diversity of topics and ideas, scientific breakthroughs, and personal experiences, starting with a brief note home in his first days as a doctoral student and concluding with a letter to a stranger seeking his guidance decades later. The result is a beautiful de facto guide to life and an eloquent testament to the human thirst for knowledge at all levels. It includes missives to and from scientific giants as well as letters to and from friends, family, students, crackpots, and regular people yearning for Feynman’s wisdom and counsel. Feynman recently remarked that “people are greatly amused” when they are given the opportunity to comprehend even a small portion of something they previously did not comprehend. These letters, which his daughter Michelle edited and annotated, not only help us understand Feynman’s enduring appeal but also brilliantly demonstrate the benefits of an inquisitive eye. His commitment to clarity, grace, humor, and optimism is palpable whether he is speaking about the Manhattan Project or advancements in quantum physics, the Challenger inquiry or elementary school textbooks, the love he has for his wife, or the best way to solve a problem.